It is known to use electrically controlled switches, often formed by field effect transistors (FETs) to control the propagation of signals from one place to another.
The impedance of a FET is typically controlled by the gate to source voltage between its gate and source terminals. The gate voltage is often derived from a control circuit and is therefore often constrained to switch between two values corresponding to having the switch “on” and having the switch “off”. As a result of this constraint, a variation in the DC voltage at the source terminal of the FET has the potential to modify the operation of the FET. It is typically undesirable that the state of the FET might be changed by the DC conditions at its signal inputs. Aspects of this disclosure relate to methods and apparatus for addressing this problem.